Internal-combustion engines – Four-cycle – Single poppet valve
Reexamination Certificate
2000-07-21
2003-04-15
Mohanty, Bibhu (Department: 3765)
Internal-combustion engines
Four-cycle
Single poppet valve
Reexamination Certificate
active
06546902
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an intake and exhaust valve system for an internal combustion engine.
BACKGROUND OF THE INVENTION
Intake and exhaust valve systems commonly used in relation to internal combustion engines include rotary, sleeve and poppet valves. Of such valves, poppet valves are favoured and are predominantly in use. In typical arrangements, intake and exhaust poppet valves are separate from each other.
There is an inherent limitation in the size of separate intake and exhaust poppet valves that can be used, as such valves must open onto the top of the combustion chamber with which they are associated. There is a benefit in maximising the size of the valve openings onto the combustion chamber as this enhances the charge volume per unit time available for intake and exhaust processes, which leads to improved performance of the engine in terms of its efficiency and/or power output and which also provides improvements in the combustion process which can lead to a reduction in pollution. However, owing to their geometry, poppet valves cannot make effective use of the available area of the cylinder head. The valve openings thus provide constrictions to the flow of intake and exhaust fluids.
A further disadvantage with separate intake and exhaust poppet valves is the inherent asymmetric relationship of the poppet valves to the cylinder axis. As a result of the asymmetry, the fuel-air mixture is not introduced into the central region of the combustion chamber and so is not distributed evenly therein. Additionally, the exhaust gases do not discharge from the central area of the chamber. This asymmetry therefore limits the efficiencies at which the engine can perform the intake and exhaust processes.
With a view to alleviating the abovementioned disadvantages of separate intake and exhaust poppet valves of an internal combust ion engine, there have been various proposals to provide concentric intake and exhaust valve assemblies. Such proposals include the intake and exhaust valve systems disclosed in U.S. Pat. Nos. 4,957,073 (BERGERON), 4,449,490 (HANSEN), 5,355,848 (DENTON), and 4,893,592 (FALERO).
As identified in BERGERON, deficiencies of some of the prior proposals for concentric intake and exhaust valve systems include excessive mass associated with such arrangements, and loading problems caused by the relatively large surface area of the exhaust valve opening against compressed gases within the combustion chamber. BERGERON seeks to provide a concentric intake and exhaust valve system which provides an increased volume of charge per unit time through the engine per intake stroke and which also reduces the mass of the concentric valve assembly. Nevertheless, the intake and exhaust system proposed by BERGERON still presents a significant reciprocating mass which is undesirable.
FALERO utilises a concentric intake and exhaust valve system in which the outer intake valve has a hollow bell-shaped valve disc. The outer intake valve has a valve stem connected to the bell-shaped valve disc by radial arms, with the radial arms and the adjacent end of the valve stem being located within the confines of the bell-shaped valve disc. The bell-shaped valve disc has a generally cylindrical side wall with a flanged portion at the free end of the side wall to sealing contact with a valve seat and an inwardly curved section at the other end of the side wall. The cylindrical side wall slidingly engages an inner generally cylindrical surface defined by a somewhat annular projection positioned between the intake and exhaust ports. The annular projection co-operates with the cylindrical side wall of the bell-shaped valve disc to maintain separation between the intake and exhaust ports during movement of the outer intake valve.
FALERO does not address the problem of reciprocating mass, as is apparent from the size of the bell-shaped valve disc. Indeed, the intake and exhaust valve system proposed by FALERO utilises an arrangement in which the axial length of the side wall of the bell-shaped valve disc exceeds the axial length of the cylindrical surface on the annular projection.
There is no apparent need for the side wall of the bell-shaped valve disc to be of such length, unless the inwardly curved section at the end thereof opposed to the flanged portion is also required to seat against the annular projection when the valve is in the closed condition.
In any event, the size of the cylindrical side wall on the bell-shaped valve disc is disadvantageous in that it provides the valve with a significant reciprocating mass which is undesirable.
A further disadvantage of FALERO is location of the radial arms connecting the bell-shaped valve disc. Because the adjacent end of the valve stem is located within the confines of the hollow bell-shaped valve disc through which there is fluid flow, the presence of the valve stem can have the effect of reducing the cross-sectional flow area within the valve, so providing a restriction to flow.
A still further disadvantage of FALERO is that the annular projection forming the cylindrical surface cannot be readily refurbished or replaced in the event of excessive wear or damage.
SUMMARY OF THE INVENTION
The present invention seeks to provide an intake and exhaust valve system which has a reduced reciprocating mass in comparison to the prior art referred to above or at least provides a useful choice as an alternative to such prior art proposals. The present invention provides an intake and exhaust valve system for an internal combustion engine having a combustion chamber within a cylinder closed at one end by a cylinder head, the valve system comprising a cavity in the cylinder head opening onto the combustion chamber through a first port; a valve assembly comprising first and second valves one of which is an intake valve movable between open and closed conditions for controlling intake fluid flow into the combustion chamber and the other of which is an exhaust valve movable between open and closed conditions for controlling exhaust gas flow from the combustion chamber; the first valve comprising a valve head sealingly engagable with the first port and a skirt structure; the skirt structure being in sliding and sealing engagement with a wall structure within the cavity whereby the skirt and wall structures cooperate to divide the cavity into an inner cavity section and an outer cavity section surrounding the inner cavity section; a first flow passage communicating with the outer cavity section; and a second flow passage communicating with the inner cavity section; the second valve being disposed in the first valve for opening and closing a second port in the first valve for controlling fluid flow between the combustion chamber and inner cavity section; wherein the skirt structure has a first axial length and the tubular wall structure has a second axial length, the first axial length being less than the second axial length.
This arrangement provides a concentric intake and exhaust valve system with reduced reciprocating mass in comparison to the prior art proposals referred to hereinbefore. The reduction in reciprocating mass is accomplished by an arrangement: (a) which utilises the skirt structure (which forms part of the reciprocating mass) and the wall structure (which does not form part of the reciprocating mass) to separate the intake and exhaust gas flow paths; and (b) in which the axial length of the skirt structure is less than the axial length of the wall structure. Indeed, it is desirable to endeavour to have the axial length of the skirt structure as small as possible so as to minimise reciprocating mass, while of course maintaining an effective length having regard to factors such as height of valve lift and sealing integrity between the wall structure and the skirt structure. The skirt structure is preferably cylindrical, as is also the face of the wall structure with which the skirt structure slidingly and sealingly engages.
The skirt structure may be sealingly engagable with the wall structure by way of any suitable means su
Ax-Tec Pty. Ltd.
Dougherty Clements & Hofer
Mohanty Bibhu
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